The activities of this focal point are concentrated on the following, multiply interrelated topics:

• Compliant mechanisms and solid-state hinges
• Modelling and characterisation of  Shape-Memory-Alloys (SMA); analysis and synthesis of passive and active mechanical SMA components
• Aeroelasticity and active aeroelastic systems
• Mathematical modelling of Electroactive Polymers (EAP)
• Modelling, design and test of solid-state actuators of other kind (e.g. piezoelectric)

Compliant systems are a peculiar class of mechanical systems designed to produce controllable large deformations by exploiting structural flexibility. They can be seen as a blend between structures (elastically deformable, but only up to a limited extent) and mechanisms (large deformations, but produced by means of localized sliding elements like bearings and hinges and not by elastic deformations). Compared to conventional mechanisms, compliant systems offer large advantages including absence of wear and backlash, reduced noise, absence of particle release, easier maintenance and manufacturing, better scalability and accuracy. Even if compliant solutions are state of the art in small-scale, precision equipment, they are strongly underrepresented in other application fields, mainly due to their inherent complexity in analysis and design. The SMS group develops compliant solutions for products of different industrial sectors (e.g. surgery instrumentation, sport articles, eye glasses, furniture, prostheses and so on) in close cooperation with industrial partners and with the Center of Structure Technologies at ETH Zürich. This project is supported by the Gebert-Rüf Stiftung.

Active aeroelastic structures are shape-adaptable airfoils which exploit aerodynamic forces to produce the desired shape changes. Since aerodynamics is, in turn, essentially influenced by the airfoil geometry, the shape changes are the result of an aeroelastic equilibrium. In the neighbourhood of static aeroelastic instabilities the interaction with the fluid can lead to strong amplification effects, which essentially reduces the performance requirements of the primary actuators, in charge of controlling the aeroelastic equilibrium. This allows for the use of active materials with relatively poor static specific performance, like piezoceramics. Within the group thorough investigations of this frontier technology are performed, ranging from the nonlinear analysis of aeroelastic equilibrium and stability, analysis and experimental verifications of active aeroelastic airfoils with simple geometry as well as the use of structures with selectable stiffness. The motivation for this work lies in the large efficiency improvement and system weight reduction which can be expected by a highly integrated, multifunctional material system, in which the main actuator is, so to say, outsourced and only a light, compact actuator system is necessary on the airfoil itself. Besides long-term applications in aerospace engineering this technology is expected to be exploitable also in other fields like energy technology (e.g. wind turbine or compressor blades) and civil engineering (e.g. aerodynamic actuators for bridge vibration control).

A highly challenging application of compliant systems is the realisation of innovative airfoils for aircraft, able to enhance performance through extended geometry control. The underlying design task is rendered highly complex by the need of keeping weight low: Conventional lightweight structures typically exploit membrane stress loading and are therefore inherently provided with low deformability. In this framework, the SMS group works on proper design solutions and develops analysis and synthesis tools able to cope with this complex requirement scenario. The main advantages which can be expected by lightweight shape-adaptable airfoils are a more efficient control of the rigid-body resultants (better manoeuvrability, enhanced aerodynamic efficiency and consequently reduced fuel consumption and emissions) and of the load distribution (structural alleviation and consequent savings in structural weight). This technology has a broad potential which extends far beyond aeronautics: Wind power generators, gas and steam turbines as well as civil engineering constructions (e.g. bridges) can profit from enhanced efficiency and improved aerodynamic performance in the view of a sustainable, energy demanding and safe development.

Shape Memory Alloys are a material class of unique characteristics: the Shape-Memory effect allows for the realisation of thermally activated actuators with very high energy-to-volume and energy-to-weight ratio; due to the so-called superelastic behaviour components can be realized which can be subject to very high level of reversible strain; finally, the large hysteresis of some alloys can be exploited to absorb large quantity of mechanical energy (passive damping and/or impact absorption). Within this task, the SMS group performs with investigations on SMA- or SMA-coated blades for gas and/or steam turbines. Multiple effects are investigated, like enhanced structural damping (aiming at reducing aeroelastic vibrations), impact absorption (e.g. bird strike), influence on fatigue behaviour and finally active shape control (with the target of improving aerodynamic efficiency).

Electroactive Polymers represent one of the excellence topics at Empa (Group “Elektroaktive Polymere"). The SMS group plans contributes to this new and challenging research field with investigations on the constitutive behaviour of the polymer, the actuator modelling as well as the characterisation of degradation mechanisms to better predict and enhance the reliability and the service life of EAPs. The motivation of this work arises from the fact that while feasibility of EAP actuators with high energy density and activation strain was demonstrated as a result of previous work, serious damage and degradation problems arose, which are still unsolved and not well understood.

Dr Flavio Campanile
Group Leader (SMS)
Mechanics for Modelling & Simulation
EMPA - Materials Science & Technology
Überlandstrasse 129
CH-8600 Dübendorf
Tel: +41 44 823 5703
Fax: +41 44 823 4252
EMail: flavio.campanile@empa.ch

Publications and Conference Proceedings